There is no op-amp--it's totally transistorized. Very simple circuit, just too much power, which is something unusual in this industry.

I rigged it with a stereo pot on the input side, and I did solve some of the problems, however, it was obviously not designed for the application for which I had hoped it would apply. Consequently, I had a good offer from Bill Grosse in Alabama, and I packed it up to be shipped to him in the morning. Bill has a lot more time, expertise and patience than I, and maybe he can come up with something.

Thanks for the response everyone,

Gary